Re: my bravo outdrive gear experiment
 

Nice Smitty. Do I hear patent gear process for Mercury? Don't forget us little people!!

Update?
 

How have these bravo mods held up?

I'm looking to amp up my motors with boost, but, drive mods might be in order to keep parts flying in close formation of one another.

I read some interesting things in this thread. Being a design engineer, I can appreciate the good thoughts. Someone had mentioned a "coating" that is 90 Rc. If it is the coating I'm thinking of, it is called XADC patented by Armolloy of IL. I've dealt with these guys and the coating has very impressive characteristics. They guarantee 95 RC min. It has a low coefficient of friction of 0.09. It is a thin dense chrome with diamond particulate...goes on with about 0.0002-0.0005" thickness. Good for reducing contact stresses on gear teeth. However, it does nothing for bending stiffness of the tooth. As with all coatings, beware of the 95 Rc hardness claim. At the end of the day, the hardness is only as good as the base material hardness. Most steels won't get much past 60 Rc with reasonable fatiguing characteristics. Go to 70 Rc, and you will have glass gears ready to shatter with the slightest impact load.

The reason the Bravo drive only has 0.010" case hardening is.. this is the best penatration depth for fatigue life with reasonable tooth stiffness. Yes, you can thru harden to bump up the static ratings, but the fatigue life will be reduced considerably. Where this cross-over point is for a modified sweet spot...dunno. If I had access to a gear program, I could tell ya what torque can be put into for some reduced fatigue life as a function of case hardness thickness.

Anyhoo....please post updates. I'm interested in some real world results and I'm sure the rest of the boating community would love to learn more about modded Bravo 1 drives as opposed to the unobtainable speedmaster option.

Smitty, it is time for an update, how are your mods holding up?

My boat is still apart (Motor freshening) but I did gears for guys in australia that ran them all winter with good results,a couple with serious single engine power. In a few weeks I'll be running again too plus I did up gears for about 20 different boats state side,haven't heard anything good or bad back yet,Smitty

BBB
Your right, the top box ratio change lowered the torque transmitted to the lower unit on an Alpha.
The critical measurement in the lower unit is the lever that you would measure between the driveshaft centerline and where the tooth contact is.
Changing this measurement will reduce tooth loading and you do this by upping the ratio ( on a Bravo) as the lever gets longer i.e. the pinion gear has a larger diameter and or you up the top box gears to reduce the torque.

The two sets you did for me are doing fine so far:D

Smitty - My Scarab Excel is holding up fine - Gained about 3 MPH switching from the 1:36 to 1:50 gears.

I'm glad to hear that,your imco lower I set-up was a beautiful piece,I'm thinking about getting one for my boat. I will be adding another step to the gear process in next few weeks,a thin ,very hard coating with near zero friction coeffiecient,it looks real promising although the current treatment seems to be working pretty well for most the guys I have worked with. I recently boosted my hp and tq over a 1000 hp and ft lbs,it will be the real test although I'm worried shafts and other parts may start catastrophicly failing,Smitty

:cool-smiley-011:
I might just send you my lowers and have you set them up since I read you do rear ends for 20+ years.

Are you tearing up lower gears,Smitty